1. Field of the Invention
The present invention relates to trigger switches, in particular, to a trigger switch for controlling a direct current (DC) motor of a rechargeable electrical power tool.
2. Description of the Related Art
The rechargeable electrical power tool for controlling the rotation number of a motor that drives a distal end tool according to the pull-in amount of a trigger is normally manufactured with a trigger switch in which the trigger and a control circuit of the motor are packaged incorporated therein.
As disclosed in Japanese Patent Application Laid-Open No. 2006-218605, the rechargeable electrical power tool includes a motor on the upper part and a battery on the lower part of a grip accommodating the trigger switch. A pair of power supply terminals for connecting a power supply is thus arranged at the lower end of the trigger switch, and an output terminal for connecting the motor is arranged on the upper part.
As disclosed in Japanese Patent Application Laid-Open No. 2006-218560, an insulating wall for isolating the power supply terminals is arranged between the two power supply terminals to prevent one part of a stranded wire or a solder forming an electrical wire from projecting out or being stringy and contacting the other power supply terminal thereby causing short-circuit when connecting the electric wires to the respective power supply terminals.
The signal line is sometimes desired to be derived from the trigger switch to connect to an auxiliary device for providing additional function to the electrical power tool such as lighting system that operates according to the pull-in amount of the trigger as disclosed in Japanese Patent Application Laid-Open No. 2001-25982.
FIG. 15 shows a conventional trigger switch 100 provided with additional function. The trigger switch 100 includes two halved housings 101a, 101b made of insulating body for accommodating circuit components, and a trigger 102 arranged projecting from the housings 101a, 101b, where a pair of power supply terminals 103a, 103b and a pair of lead wires 104a, 104b output to the auxiliary device such as lighting system and control device are arranged lined with each other along the seam of the housings 101a, 101b at the lower end.
The power supply terminals 103a, 103b and the lead wires 104a, 104b are desirably derived from the seam of the housings 101a, 101b to maintain dust resistance. Since the current output to the auxiliary device is small, insulation electric wire having a narrow wire diameter may be used for the lead wires 104a, 104b, and may be derived so as to be arranged vertically in a direction orthogonal to the seam of the housings 101a, 110b as shown in the figure.
An inter-terminal insulating wall 105 formed by extending the housings 101a, 101b is arranged between the power supply terminal 103a and the power supply terminal 103b, and a lead wire insulating wall 106 formed by extending the housings 101a, 101b is arranged between the power supply terminal 103a and the lead wires 104a, 104b. 
As shown in the figure, the inter-terminal insulating wall 105 must have a sufficient height so that one part of the stranded wire or the solder forming the electric wires 107a, 107b do not project out or become stringy, thereby short circuiting the power supply terminals 103a, 103b when connecting the electrical wires 107a, 107b to the respective power supply terminals 103a, 103b, and normally, must have a thickness of at least about 1 mm to ensure strength. Similarly, the lead wire insulating wall 106 normally requires a thickness of about 1 mm. The lead wires 104a, 104b may be insulation electric wires having a conductor cross sectional area of about 0.2 mm2, and an outer diameter of about 1.5 mm. Furthermore, a boss (guide) 108 having a thickness of about 1 mm is formed at the housings 101a, 101 b projecting out from the housings 101a, 101b to surround the lead wires 104a, 104b so that stress does not concentrate at the derived portion of the lead wires 104a, and 104b. 
The lead wire insulating wall 106, the lead wires 104a, 104b, and the guide 108 arranged to add the auxiliary device to the electrical power tool occupy a length of about 3.5 mm in total at the bottom surface of the trigger switch 100. There is, however, a demand to narrow the grip as much as possible to enhance the operability of the electrical power tool. Thus, the bottom area required to derive the lead wires 104a, 104b is desirably set small, in particular, the length in the direction along the seam of the housings 101a, 101b is desirably set small in the trigger switch 100.